Fuel injector driver

[Jinx-4]

I've got a job to look into and would appreciate anyone being able to
share practical knowledge/experience

The project involves a squirt of 'camping gas' (butane/propane mix -
LPG) from a canister into a cylinder. This is then ignited by a spark
plug or piezo. The explosion drives a piston very forcibly, stretching
the return spring which brings it back to its rest position, mostly venting
the exhaust as it does. It's similar to a gas nail gun (like the Paslode),
only bigger. Operation is not more often than once per minute. It has
been used in an unrefined version, proving the principle, and now I've
got it to improve the performance. On improvement for example is
linking temperature and pressure to injection time to try and get a
reliable and consistent bang, and there'll be a PIC to do this amongst
other things

The first thing I need to do is find out some characteristics of fuel
injection valves. A Google for fuel injector driver brings up for example
these two

(1) http://www.bgsoflex.com/FI_tester_doc.pdf

(2) http://bakengineering.com/page6.html

The figures in (1) are in the general ballpark of activation times based
on rough rpm calculations I did. (2) indicates that 30V is being applied

"The POWER-DRIVER outperforms other peak-hold fuel injector
driver modules! While other modules use 12 Volts (supplied by the
battery) to drive the injectors to 4 Amperes, ours are voltage-boosted
and deliver 30V, for significantly faster fuel injector response time"

Using over-voltage is something I'd already considered to improve
reaction time, so it's good to see that it's actually done in practice. I'm
assuming that something like a low-side FET is used

I've not yet got the pressure figures for a typical gas canister (although
800psi has been suggested) so the actual activation time range for a
valve in this application is an uncertainty

I'm still Googling but if anyone has something they'd like to share it
would be appreciated

TIA

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[John Gardner-3]

Vapor pressure at 86 deg F:

Propane - 166 psi
Butane - 41 psi

Construction of typical camping gas cylinders suggest contents is
primarily Butane, with a skoche of Propane to keep some positive
pressure in the cylinder at or near freezing temps.

Propane tank safety valves are designed to vent at circa 300 psi, IIRC.

800 psi seems unlikely. Hope this helps.

Jack
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[Jinx-4]

> Vapor pressure at 86 deg F:
>
> Propane - 166 psi
> Butane - 41 psi
>
> Construction of typical camping gas cylinders suggest contents is
> primarily Butane, with a skoche of Propane to keep some positive
> pressure in the cylinder at or near freezing temps.
>
> Propane tank safety valves are designed to vent at circa 300 psi, IIRC.
>
> 800 psi seems unlikely. Hope this helps.

It does, thanks. The 800psi was suggested by the person I'm helping
and he hasn't done too much technical research. I suggested back
that he take a canister to a gas supplier (eg BOC or Air Liquide) and
see if they can measure the pressure

The low temperature pressure is of interest as the product will be working
in any outdoor climate. I mentioned Paslode brand nail guns. They've
introduced a smart metering system for their nail guns, as until now their
guns are not reliable in cold conditions. I've seen the module which can
be retro-fitted but unfortunately it's encased in epoxy. It doesn't appear
to measure gas pressure, likely just temperature, and presumably there's
a micro with a look-up table based on gas laws to set the valve open time

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[John Gardner-3]

Been awhile, but I've used Cherry Semiconductor injector drivers.
They worked as advertised - Don't remember any problems.

Think I still have a few somewhere. I'll look around.
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